Social Security Card
This is the number one thing to not keep in your wallet. If a thief gets a hold of your Social Security card, he can open credit cards, take out loans, or even buy a car—it makes you very vulnerable to identity theft. There is no need to carry this around as an extra form of ID, and even the U.S. government's website recommends leaving your card at home in a safe place. Your Social Security number is only nine digits—just memorize it.